Linear Regulating of Polymer Acceptor Aggregation with Short Alkyl Chain Units Enhances All‐Polymer Solar Cells’ Efficiency

Abstract The power conversion efficiency (PCE) of all‐polymer solar cells (all‐PSCs) has ascended rapidly arising from the development of polymerized small‐molecule acceptor materials. However, numerous insulating long alkyl chains, which ensure the solubility of the polymer, result in inferior aggregation and charge mobility. Herein, this study proposes a facile random copolymerization strategy of two small molecule acceptor units with different lengths of alkyl side chains and synthesizes a series of polymer acceptors PYT‐EH x , where x is the percentage of the short alkyl chain units. The aggregation strength and charge mobility of the acceptors rise linearly with increasing the proportion of short alkyl chain units. Thus, the PYT‐EH20 reaches balanced aggregation with the star polymer donor PBDB‐T, resulting in optimal morphology, fastest carrier transport, and reduced recombination and energy loss. Consequently, the PYT‐EH20‐based device yields a 14.8% PCE, a 16% improvement over the control PYT‐EH0‐based device, accompanied by an increase in open‐circuit voltage ( V oc ), short‐circuit current density ( J sc ), and fill factor (FF). This work demonstrates that the random copolymerization strategy with short alkyl chain insertion is an effective avenue for developing high‐performance polymer acceptors, which facilitates further advances in the efficiency of all‐PSCs.